Computer Programming Concepts and Visual Basic David I. Schneider

‘The density (number of people per square mile)
‘will be displayed rounded to a whole number
rawDensity = pop / area
density = Round(rawDensity) ‘round to whole number
picDensity.Print “The density of “; state; “ is”; density;
picDensity.Print “people per square mile.”
End Sub
[Run, and then click the command button. The following is displayed in the picture box.]
The density of Hawaii is 183 people per square mile.
The density of Alaska is 1 people per square mile.
The parameters in the density program can have any names, as with the parameters in
the addition program of Example 3. The only restriction is that the first parameter be a string
variable and that the last two parameters be numeric variables. For instance, the Sub procedure
could have been written
Private Sub CalculateDensity(x As String, y As Single, z As Single)
Dim rawDensity As Single, density As Single
‘The density (number of people per square mile)
‘will be rounded to a whole number
rawDensity = y / z
density = Round(rawDensity)
picDensity.Print “The density of “; x; “ is”; density;
picDensity.Print “people per square mile.”
End Sub
When nondescriptive names are used for parameters, the Sub procedure should contain
comments giving the meanings of the variables. Possible comments for the preceding program
are
‘x name of the state’
y population of the state’
z area of the state
■ VARIABLES AND EXPRESSIONS AS ARGUMENTS
The items appearing in the parentheses of a Call statement are called arguments. These should
not be confused with parameters, which appear in the heading of a Sub procedure. In Example
3, the arguments of the Call Add statements were constants. These arguments also could have
been variables or expressions. For instance, the event procedure could have been written as follows.
See Figure 3-1.
Private Sub cmdAdd_Click()
Dim x As Single, y As Single, z As Single
‘Display the sum of two numbers
picResult.Cls
Call ExplainPurpose
picResult.Print
x = 2
y = 3
Call Add(x, y)
Call Add(x + 2, 2 * y) z = 7
Call Add(z, z + 1)
End Sub
Sub Procedures, Part I 77